The Moncton weather forecast called for a marked decrease in ceiling and visibility starting at 0300; however, this transition was already underway when Flight620 flew the first approach at about 0230. The crew were unable to see the runway environment at the MDA of 270feet agl, while the 0200ATIS information stated that the ceiling was 1100feet with a visibility of 10sm. On the second approach, the crew did not see the runway lights until they had descended to 200feet agl, at about 0240. The reported weather remained unchanged until after the second approach. A weather special released at 0249reported that ceiling and visibility were 1100feet and 1sm. By this time the crew had already commenced their third approach, and they did not receive the 0249report. Although the deterioration in the weather had been accurately forecast for this period, the frequency of the observations were not adequate to capture the weather deterioration. The decrease in ceiling and visibility was not detected by either the controllers or the weather observers, and no special observation was requested until after the second missed approach. The provision of more data to the weather observer, such as forecasts or pilot reports, might have prompted additional check observations. Also, better guidance as to when additional check observations are required, including specific reference to the consideration of forecasts, temperature/dew point spread, etc. might have ensured the completion of additional check observations so that the change in visibility would have been detected prior to Flight620's first approach. Valid weather information is a critical element in good pilot decision making. When the destination weather is reported to be at or near minimums, crews update weather information, choose the approach most likely to be successful, and make plans for a possible diversion prior to the approach at destination. However, when the destination weather is reported to be well above minimums, crews anticipate a successful approach and landing and may forgo alternate planning and choose the most expedient approach likely to be successful. The Moncton 0200 weather report received during descent for the first approach was as follows: estimated 1100feet overcast, visibility 10sm. Based on this report, the crew planned for and executed a straight-in, localizer back-course approach to Runway11, anticipating no difficulties. Consequently, they did not plan for a diversion, and the approach choice was based upon the most expedient approach for the reported weather conditions. Had the reported weather reflected the actual lowered ceiling and visibility, the crew would likely have planned for a diversion and conducted an ILS approach to Runway29 as their first approach. This option would have increased the chances of landing successfully on the first approach and avoided the low fuel state. From post-flight calculations, there was enough fuel on board to allow a second approach. Although the aircraft was not laterally positioned to land on the second approach, the captain did not intervene to reject the landing until the aircraft was in a substantial left-wing down attitude, very near the runway surface, with power reduced. During the rejected landing the aircraft's wings were not leveled until after the nose was raised, resulting in the left wing contacting the runway. After the rejected landing there was min div fuel on board. At this time, the captain was faced with the decision to attempt a third approach in known conditions or proceed to the alternate airport without up-to-date weather information. Potentially, they could arrive at the alternate with a worse fuel state and in adverse weather conditions. The decision to attempt the third approach was inconsistent with the intent of the FOM. However, the captain was well aware of the weather conditions and that an imminent landing at Moncton was reasonably assured.Analysis The Moncton weather forecast called for a marked decrease in ceiling and visibility starting at 0300; however, this transition was already underway when Flight620 flew the first approach at about 0230. The crew were unable to see the runway environment at the MDA of 270feet agl, while the 0200ATIS information stated that the ceiling was 1100feet with a visibility of 10sm. On the second approach, the crew did not see the runway lights until they had descended to 200feet agl, at about 0240. The reported weather remained unchanged until after the second approach. A weather special released at 0249reported that ceiling and visibility were 1100feet and 1sm. By this time the crew had already commenced their third approach, and they did not receive the 0249report. Although the deterioration in the weather had been accurately forecast for this period, the frequency of the observations were not adequate to capture the weather deterioration. The decrease in ceiling and visibility was not detected by either the controllers or the weather observers, and no special observation was requested until after the second missed approach. The provision of more data to the weather observer, such as forecasts or pilot reports, might have prompted additional check observations. Also, better guidance as to when additional check observations are required, including specific reference to the consideration of forecasts, temperature/dew point spread, etc. might have ensured the completion of additional check observations so that the change in visibility would have been detected prior to Flight620's first approach. Valid weather information is a critical element in good pilot decision making. When the destination weather is reported to be at or near minimums, crews update weather information, choose the approach most likely to be successful, and make plans for a possible diversion prior to the approach at destination. However, when the destination weather is reported to be well above minimums, crews anticipate a successful approach and landing and may forgo alternate planning and choose the most expedient approach likely to be successful. The Moncton 0200 weather report received during descent for the first approach was as follows: estimated 1100feet overcast, visibility 10sm. Based on this report, the crew planned for and executed a straight-in, localizer back-course approach to Runway11, anticipating no difficulties. Consequently, they did not plan for a diversion, and the approach choice was based upon the most expedient approach for the reported weather conditions. Had the reported weather reflected the actual lowered ceiling and visibility, the crew would likely have planned for a diversion and conducted an ILS approach to Runway29 as their first approach. This option would have increased the chances of landing successfully on the first approach and avoided the low fuel state. From post-flight calculations, there was enough fuel on board to allow a second approach. Although the aircraft was not laterally positioned to land on the second approach, the captain did not intervene to reject the landing until the aircraft was in a substantial left-wing down attitude, very near the runway surface, with power reduced. During the rejected landing the aircraft's wings were not leveled until after the nose was raised, resulting in the left wing contacting the runway. After the rejected landing there was min div fuel on board. At this time, the captain was faced with the decision to attempt a third approach in known conditions or proceed to the alternate airport without up-to-date weather information. Potentially, they could arrive at the alternate with a worse fuel state and in adverse weather conditions. The decision to attempt the third approach was inconsistent with the intent of the FOM. However, the captain was well aware of the weather conditions and that an imminent landing at Moncton was reasonably assured. The captain's decision to intervene and reject the landing on the second approach was too late to prevent the aircraft from contacting the runway surface. The aircraft's wings were not leveled until after the nose was raised, resulting in the left wing contacting the runway.Findings as to Causes and Contributing Factors The captain's decision to intervene and reject the landing on the second approach was too late to prevent the aircraft from contacting the runway surface. The aircraft's wings were not leveled until after the nose was raised, resulting in the left wing contacting the runway. The forecasted deteriorating weather was not detected or reported in a timely manner.Finding as to Risk The forecasted deteriorating weather was not detected or reported in a timely manner. The aircraft landed with less than the minimum diversion fuel required in the Flight Operations Manual (FOM); however, the decision to carry out the third approach could be considered reasonable in the circumstances faced by the captain. The weather conditions reported to the crew were not representative of the actual weather conditions at the airport. This contributed to the planning errors made by the crew and the unnecessarily low fuel state.Other Findings The aircraft landed with less than the minimum diversion fuel required in the Flight Operations Manual (FOM); however, the decision to carry out the third approach could be considered reasonable in the circumstances faced by the captain. The weather conditions reported to the crew were not representative of the actual weather conditions at the airport. This contributed to the planning errors made by the crew and the unnecessarily low fuel state. The section dealing with minimum required diversion fuel in the operator's FOM has been amended. The amended version reads as follows: Upon reaching MIN DIV fuel, the flight MUST proceed immediately to the alternate airport. Transport Canada is proposing changes to the Canadian Aviation Regulations that will define the use of pilot-monitored approaches as part of the new approach ban regulations. In response to this occurrence, Transport Canada regional staff conducted an inspection of the weather observation service at Moncton on 05October2004. As a result of the findings, the flood lights near the ceiling projector were adjusted to reduce interference with weather observations, and NAV CANADA has implemented new procedures to improve the communication of information related to changing weather conditions between the weather office and the tower personnel.Safety Action The section dealing with minimum required diversion fuel in the operator's FOM has been amended. The amended version reads as follows: Upon reaching MIN DIV fuel, the flight MUST proceed immediately to the alternate airport. Transport Canada is proposing changes to the Canadian Aviation Regulations that will define the use of pilot-monitored approaches as part of the new approach ban regulations. In response to this occurrence, Transport Canada regional staff conducted an inspection of the weather observation service at Moncton on 05October2004. As a result of the findings, the flood lights near the ceiling projector were adjusted to reduce interference with weather observations, and NAV CANADA has implemented new procedures to improve the communication of information related to changing weather conditions between the weather office and the tower personnel.